public class Fenshu {
    public static void main(String[] args) {
        double ret = 0;
        double ret1 = 0;
        double ret2 = 0;
        for (int i = 1; i <= 100; i++) {
            if(i % 2 != 0){
                ret1 += 1.0/i;
            }
            else{
                ret2 += -1.0/i;
            }
        }
        ret = ret1 + ret2;
        System.out.println(ret);
    }
}
